Low-cost Receivers Research Articles

Wide-Band Interference Mitigation in GNSS Receivers Using Sub-Band Automatic Gain Control.

The performance of global navigation satellite system (GNSS) receivers is significantly affected by interference signals. For this reason, several research groups have proposed methods to mitigate the effect of different kinds of jammers. One effective method for wide-band interference mitigation (IM) is the high-rate DFT-based data manipulator (HDDM) pulse blanker (PB). It provides good performance to pulsed and frequency sparse interference. However, it and many other methods have poor performance against wide-band noise signals, which are not frequency-sparse. This article proposes to include automatic gain control (AGC) in the HDDM structure to attenuate the signal instead of removing it: the HDDM-AGC. It overcomes the wide-band noise limitation for IM at the cost of limiting mitigation capability to other signals. Previous studies with this approach were limited to only measuring the carrier-to-noise density ratio () performance of tracking, but this article extends the analysis to include the impact of the HDDM-AGC algorithm on the position, velocity, and time (PVT) solution. It allows an end-to-end evaluation and impact assessment of mitigation to a GNSS receiver. This study compares two commercial receivers: one high-end and one low-cost, with and without HDDM IM against laboratory-generated interference signals. The results show that the HDDM-AGC provides a PVT availability and precision comparable to high-end commercial receivers with integrated mitigation for most interference types. For pulse interferences, its performance is superior. Further, it is shown that degradation is minimized against wide-band noise interferences. Regarding low-cost receivers, the PVT availability can be increased up to 40% by applying an external HDDM-AGC.

Applicability of Cost-Effective GNSS Sensors for Crustal Deformation Studies.

The geodetic monitoring of the continuous crustal deformation in a particular region has traditionally been the prerogative of the scientific communities capable of affording high-price geodetic-class instruments to track the tiny movements of tectonic plates without losing precision. However, GNSS technology has been continuously and rapidly growing, and in the last years, new cost-efficient instruments have entered the mass market, gaining the attention of the scientific community for potentially being high-performing alternative solutions. In this study, we match in parallel a dual-frequency low-cost receiver with two high-price geodetic instruments, all connected to the same geodetic antenna. We select North-East Italy as testing area, and we process the data together with the observations coming from a network of GNSS permanent stations operating in this region. We show that mm-order precision can be achieved by cost-effective GNSS receivers, while the results in terms of time series are largely comparable to those obtained using high-price geodetic receivers.

Sensing Real-Time Water Vapor Over Oceans With Low-Cost GNSS Receivers

Water vapor over oceans is significant for numerical weather prediction (NWP) and climate research. Ocean platform-based global navigation satellite system (GNSS) which can sense the atmospheric water vapor is becoming an important supplement for water vapor measurements over oceans. However, the application of ocean platform-based GNSS meteorology is normally based on geodetic GNSS receivers, which implies the high cost of hardware. In this contribution, we investigate the potential of retrieving real-time water vapor over oceans with a low-cost receiver (u-blox F9P), and a geodetic GNSS receiver (Trimble NetR9) is also equipped in the experiment vessel. The post-processed Trimble NetR9 zenith total delay (ZTD) estimates and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 precipitable water vapor (PWV) products are used for the validation of real-time ZTDs and PWV values. The results show that the real-time ZTDs derived from the low-cost multi-GNSS (GPS + Galileo) observations obtain a difference of over 2.13 cm in root-mean-square (RMS) compared to the post-processed ZTDs with an averaged initialization time of approximately 40 mins. In addition, compared to ERA5 PWV, the real-time PWV derived from u-blox F9P multi-GNSS observations shows a difference in RMS of approximately 4 mm. Although u-blox F9P multi-GNSS performs relatively worse than Trimble NetR9 multi-GNSS in real-time ZTD/PWV estimates, the accuracy of low-cost GNSS receivers derived water vapor over oceans can still meet the requirements for NWP and nowcasting, which demonstrates promising prospects in supplementing the measurements of water vapor over oceans.

Applicability of NeQuick G ionospheric model for single-frequency GNSS users over India

<abstract> <p>The major source of error in the positioning of GNSS is from the region of Ionosphere. The single-frequency GNSS receiver cannot eliminate the ionospheric error due to dispersive medium and frequency-dependent. The low-cost GNSS receivers are highly dependent on single-frequency approaches of Ionosphere region popularly known as Klobuchar, NeQuick G, and BDS2 methods to estimate the data of position, velocity and time. The regional satellite navigation system of India, known as Navigation with Indian Constellation (NavIC) adopted ionospheric models based on single-frequency namely, Klobuchar and grid-based correction models. The Klobuchar modelos accuracy is less for predicting ionospheric delays in low latitude regions like India under Equatorial Ionization Anomaly (EIA) conditions. In this paper, the NeQuick G modelos applicability for NavIC users over the Indian region is investigated. NeQuick G modelos performance is validated with dense GPS TEC network data of 26 stations spread across India and IRI-2016 model, during 2014, 2015 and 2016. The predicted TEC results indicate that EIA structures are well captured by NeQuick G and IRI-2016 models. The results indicate that both NeQuick G and IRI-2016 models well predict season asymmetry and decrease of TEC intensity due to descending phase solar cycle activity. It is found that NeQuick G is one of the contenders of single frequency ionospheric models for GNSS/NavIC users in India.</p> </abstract>

First considerations on post processing kinematic GNSS data during a geophysical oceanographic cruise

<p class="Abstract">Differential GNSS positioning on vessels is of considerable interest in various fields of application as navigation aids, precision positioning for geophysical surveys or sampling purposes especially when high resolution bathymetric surveys are conducted. However ship positioning must be considered a kinematic survey with all the associated problems. The possibility of using high-precision differential GNSS receivers in navigation is of increasing interest, also due to the very recent availability of low-cost differential receivers that may soon replace classic navigation ones based on the less accurate point positioning technique. The availability of greater plano-altimetric accuracy, however, requires an increasingly better understanding of planimetric and altimetric reference systems. In particular, the results allow preliminary considerations on the congruence between terrestrial reference systems (which the GNSS survey can easily refer to) and marine reference systems (connected to National Tidegauge Network). In spite of the fluctuations due to the physiological continuous variation of the ship's attitude, GNSS plot faithfully followed the trend of the tidal variations and highlighted the shifts between GNSS plot and the tide gauges due to the different materialization of the relative reference systems.</p><p class="Abstract"><span lang="EN-US"><br /></span></p>

Stochastic model assessment of low-cost devices considering the impacts of multipath effects and atmospheric delays

A proper stochastic model is urgently required in Global Navigation Satellite System (GNSS) data processing, whereas deficient knowledge of stochastic model often occurs, especially for low-cost devices such as low-cost receivers and smartphones. The stochastic modeling for low-cost devices considering the impacts of multipath effects and atmospheric delays is systematically studied in this paper. Firstly, two stochastic model assessment methods for low-cost devices are deduced. Secondly, the stochastic modeling including measurement precision and physical correlation for the low-cost receiver and smartphone is comprehensively investigated with single-differenced residuals by using different baseline lengths. The results show that the measurement precisions of short baseline and medium-long baseline for the low-cost receiver are worse than zero baseline due to the systematic errors. The code measurement precisions are similar between short baseline and medium-long baseline, whereas the phase measurement precisions of medium-long baseline are larger than short baseline. Moreover, the measurement precisions of the smartphone are much worse than the low-cost receiver and the C/N0-dependent function is more suitable for the smartphone measurements. For the physical correlation, the measurements of zero baseline are free of cross correlation, but the cross correlation can exist in short baseline and medium-long baseline. The phase measurements of the low-cost receiver are free of temporal correlation for zero baseline, but the code measurements show a certain temporal correlation. Meanwhile, the temporal correlations of the low-cost receiver can exist in short baseline and they are larger than zero baseline due to the multipath effects. In the medium-long baseline, the temporal correlations of code measurements are similar with short baseline both for the low-cost receiver and smartphone, whereas the temporal correlations of phase measurements become larger than short baseline. It can be concluded that the unmodeled errors such as multipath effects and atmospheric delays should be taken into account in the realistic stochastic model assessment including measurement precision and physical correlation for the low-cost devices. Meanwhile, different baseline lengths may consider the baseline-specific stochastic model better in realistic precise positioning.

Multi-constellation single-frequency ionospheric-free precise point positioning with low-cost receivers

We analyze the observation quality, assess the performance and identify the constraints of quadruple-constellation single-frequency ionospheric-free precise point positioning (SF-IF PPP) with low-cost receivers. It is revealed that low-cost receivers with patch antennas exhibit lower C/N0 records and a weaker elevation dependence of C/N0 than the high-grade equipment. The results demonstrate that low-cost receivers can offer code measurements with similar noise compared to high-grade receivers providing that the multipath effect is eliminated. Regarding positioning performance, it is shown how SF-IF PPP for the high-grade receiver converges approximately two times faster than for the low-cost receiver with a patch antenna. It is confirmed that an application of a survey-grade antenna instead of the patch one noticeably enhances the performance of low-cost receiver SF-IF PPP. The study also reveals that the multipath effect is a dominant factor that constrains the performance of SF-IF PPP with low-cost receivers.

Assessment of regularization techniques in GNSS tropospheric tomography based on single- and dual-frequency observations

Water vapor is one of the most variable components in the earth's atmosphere and has a significant role in forming clouds, rain and snow, air pollution, and acid rain. Therefore, increasing the accuracy of estimated water vapor can lead to more accurate predictions of severe weather, upcoming storms, and natural hazards. In recent years, GNSS has turned out to be a valuable tool for remotely sensing the atmosphere. In this context, GNSS tomography evolved to an extremely promising technique to reconstruct the spatiotemporal structure of the troposphere. However, locating dual-frequency (DF) receivers with a spatial resolution of a few tens of kilometers sufficient for GNSS tomography is not economically feasible. Therefore, in this research, the feasibility of using single-frequency (SF) observations in GNSS tomography as an alternative approach has been investigated. The algebraic reconstruction technique (ART) and the total variation (TV) method are examined to reconstruct a regularized solution. The accuracy of the reconstructed water vapor distribution model using low-cost receivers is verified by radiosonde measurements in the area of the EPOSA (Echtzeit Positionierung Austria) GNSS network, which is mostly located in the east part of Austria for the period DoY 232–245, 2019. The results indicate that irrespective of the investigated ART and TV techniques, the quality of the reconstructed wet refractivity field is comparable for both SF and DF schemes. However, in the SF scheme the MAE with respect to the radiosonde measurements for ART + NWM and ART + TV can reach up to 10 ppm during noontime. Despite that, all statistical results demonstrate the degradation of the retrieved wet refractivity field of only 10–40% when applying the SF scheme in the presence of the initial guess.

A Low Cost, High-Reliability Receiver System for Reading Passive RFID Tags

Radio-Frequency Identification (RFID) is one of the leading enabling technologies of the Internet of Things (IoT) at low cost and high granularity scenarios. The cost of implementing IoT applications concerns the development and operation of receiver systems for reading labels. In this paper, we propose a low-cost receiver system based on off-the-shelf components allied to the development of a microstrip antenna. The proposed system is capable of receiving and processing digital signals scattered back from a passive RFID tag. The proposal relies on a Python application embedded in Raspberry Pi hardware, in which a bank of digital filters processes the signal. The proposal separates the received signal into sub-bands and implements a decision-maker that detects and codes radiofrequency carriers’ presence in sub-bands. Simulation using artificial random noise proves that the proposed and implemented decision-maker achieves 92% reliability for a Signal-to-Noise ratio between 1.6 dB and 2.3 dB. The evaluation of the printed dipole antennas pair for the RFID receiver system indicates a return loss of 19.22 dB for operation at 915 MHz.

Performance evaluation of GNSS receiver clock modelling in urban navigation using geodetic and high-sensitivity receivers

AbstractIn urban areas, the Global Navigation Satellite System (GNSS) can lead to position errors of tens of meters due to signal obstruction and severe multipath effects. In cases of 3D-positioning, the vertical coordinate is estimated less accurately than are the horizontal coordinates. Multisensor systems can enhance navigation performance in terms of accuracy, availability, continuity and integrity. However, the addition of multiple sensors increases the system cost, and thereby the applicability to low-cost applications is limited. By using the concept of receiver clock modelling (RCM), the position estimation can be made more robust; the use of high-sensitivity (HS) GNSS receivers can improve the system availability and continuity. This paper investigates the integration of a low-cost HS GNSS receiver with an external clock in urban conditions; subsequently, the gain in the navigation performance is evaluated. GNSS kinematic data is recorded in an urban environment with multiple geodetic-grade and HS receivers. The external clock stability information is incorporated through the process noise matrix in a Kalman filter when estimating the position, velocity and time states. Results shows that the improvement in the precision of the height component and vertical velocity with both receivers is about 70% with RCM compared with the estimates obtained without applying RCM. Pertaining accuracy, the improvement in height with RCM is found to be about 70% and 50% with geodetic and HS receivers, respectively. In terms of availability, the HS receiver delivers an 100% output compared with a geodetic receiver, which provides an output 99⋅4% of the total experiment duration.

INTEGRATED GEOMATIC TECHNIQUES FOR THE LOCALIZATION AND GEOREFERENCING OF ANCIENT HERMITAGES

Abstract. Historical maps represent an important source of geographical information. The changes occurred over time can be extrapolated from them, especially if their geometric accuracies match those achievable with modern survey techniques. An 1820 map belonging to the Gregorian Cadastre provides the position of seven hermitages belonging to the monastery of Fara in Sabina (Italy). Just three of them are nowadays visible, while the others may have been covered by thick vegetation or been destroyed during the Second World War. The paper proposes the integration of geomatic techniques for the localization of the lost hermitages. To do so, Structure from Motion (SfM) algorithms were applied to UAV imagery to produce an orthophoto of the area. In addition, a GNSS survey was carried out using a professional and a low-cost receiver to correctly georeference the photogrammetric products. An accuracy assessment was then performed to evaluate the performance of the u-blox board in real applications. The accuracies obtained with the low-cost receiver indicates a possible more widespread utilization of these new devices. Subsequently, the comparison between the orthophoto and the cadastral map have been detailed. A weak correspondence between the position of the hermitages in the two maps have been observed. On the other side, the comparison led to the localization of two lost hermitages, with the other two being still undiscovered. This study has opened the door to an enhancement process of the monastery and to the rediscovery of the religious values of the hermitages.

Evaluation of Low-Cost GNSS Receiver under Demanding Conditions in RTK Network Mode

Positioning with low-cost GNSS (Global Navigation Satellite System) receivers is becoming increasingly popular in many engineering applications. In particular, dual-frequency receivers, which receive signals of all available satellite systems, offer great possibilities. The main objective of this research was to evaluate the accuracy of a position determination using low-cost receivers in different terrain conditions. The u-blox ZED-F9P receiver was used for testing, with the satellite signal supplied by both a dedicated u-blox ANN-MB-00 low-cost patch antenna and the Leica AS10 high-precision geodetic one. A professional Leica GS18T geodetic receiver was used to acquire reference satellite data. In addition, on the prepared test base, observations were made using the Leica MS50 precise total station, which provided higher accuracy and stability of measurement than satellite positioning. As a result, it was concluded that the ZED-F9P receiver equipped with a patch antenna is only suitable for precision measurements in conditions with high availability of open sky. However, the configuration of this receiver with a geodetic-grade antenna significantly improves the quality of results, beating even professional geodetic equipment. In most cases of the partially obscured horizon, a high precision positioning was obtained, making the ZED-F9P a valuable alternative to the high-end geodetic receivers in many applications.

An Improved Single-Epoch Attitude Determination Method for Low-Cost Single-Frequency GNSS Receivers

GNSS attitude determination has been widely used in various navigation and positioning applications, due to its advantages of low cost and high efficiency. The navigation positioning and attitude determination modules in the consumer market mostly use low-cost receivers and face many problems such as large multipath effects, frequent cycle slips and even loss of locks. Ambiguity fixing is the key to GNSS attitude determination and will face more challenges in the complex urban environment. Based on the CLAMBDA algorithm, this paper proposes a CLAMBDA-search algorithm based on the multi-baseline GNSS model. This algorithm improves the existing CLAMBDA method through a fixed geometry constraint among baselines in the vehicle coordinate system. A fixed single-baseline solution reduces two degrees of freedom of vehicle rigid body, and a global minimization search for the ambiguity objective function in the other degree of freedom is conducted to calculate the baseline vector and its Euler angles. In addition, in order to make up for the shortcomings of short baseline ambiguity in complex environments, this paper proposes different validation strategies. Using three low-cost receivers (ublox M8T) and patch antennas, static and dynamic on-board experiments with different baseline length set-ups were carried out in different environments. Both the experiments prove that the method proposed in this paper has greatly improved the ambiguity fixing performance and also the Euler angle calculation accuracy, with an acceptable calculation burden. It is a practical vehicle-mounted attitude determination algorithm.

Feasibility of easy-to-implement methods to analyze systematic errors of multipath, differential code bias, and inter-system bias for low-cost receivers

Feasibility of easy-to-implement methods to analyze systematic errors of multipath, differential code bias, and inter-system bias for low-cost receivers

Review on advance tubular receivers for central solar tower system

This review focused on central tubular receiver modelling to obtain concentrated solar energy. Required specifications involved with efficient low cost receiver with suitable material which able to absorb concentrated solar radiations. This type of advance receivers shows excellent performance in the commercial and domestic applications. Review shows compiles literature engaged in mechanical and thermal modelling of receiver. Also highlighted on various geometries, tube sizes and various heat transfer fluids and their effect on overall performance of receiver. Recently authors concentrated on CFD simulations of different kind of receiver and put forth advanced design which offers superior flexibility and accuracy also explains stresses generated in the tube of receiver. The selection of stress theory is impacting on the mechanical life of the receiver with different approaches presented. Extensive technical analysis is investigated on different receivers for internal and external tubular geometry. Effect of heat transfer for different geometry is also observed. In this paper different aspects discussed thoroughly like receiver design, Numerical simulation, outdoor and indoor testing facilities, thermal efficiency and desired outlet temperature, benefits, future challenges, and research needs.

Developing an Error Map for Cognitive Navigation System

Global Navigation Satellite System (GNSS) positioning is a widely used and a key intelligent transportation system (ITS) technology. An automotive navigation system is necessary when driving to an unfamiliar location. One difficulty regarding GNSS positioning occurs when an error is caused by various factors, which reduces the positioning accuracy and impacts the performance of applications such as navigation systems. However, there is no way for users to be aware of the magnitude of the error. In this paper, we propose a cognitive navigation system that uses an error map to provide users with information about the magnitude of errors to better understand the positioning accuracy. This technology can allow us to develop a new navigation system that offers a more user-friendly interface. We propose that the method will develop an error map by using two low-cost GNSS receivers to provide information about the magnitude of errors. We also recommend some applications that will work with the error map.

Enhanced fault detection and exclusion based on Kalman filter with colored measurement noise and application to RTK

With the development of high-precision safety–critical applications using global navigation satellite systems (GNSS), fault detection and exclusion (FDE) is indispensable to guaranteeing the integrity of a GNSS positioning and navigation system. Many FDE algorithms have been developed based on the standard Kalman filter (KF), assuming that GNSS measurements come with Gaussian uncorrelated white noise. The existence of colored noise in GNSS measurements, which is typical for positioning with low-cost receivers and in challenging environments will, however, degrade the performance of KF-based FDE algorithms. We proposed an FDE scheme based on improved KF considering colored noise (CKF) as a first-order autoregressive model to improve the FDE performance. The performance of the proposed CKF-based FDE algorithm was evaluated with an application to real-time kinematic positioning using a low-cost receiver. A CKF-based fault detection test, a fault identification test, a minimum detectable bias (MDB), error distribution, and positioning results were examined. The results showed that the CKF-based FDE can obtain realistic statistical information to improve integrity monitoring reliability. The fault detection test achieved a 17.83% improvement in FDE performance and a reduction in the false alarm rate, from 23.33 to 5.50%, compared with KF-based FDE. The tests also indicated that the CKF-based FDE can detect multiple faults with zero-miss detection. The fault identification test had an average improvement of 32.14%, and a more realistic MDB was obtained. The results of this study contribute to making objective decisions for the integrity monitoring of practical, precise GNSS positioning.

Reconstruction of Relative Phase of Self-Transmitting Devices by Using Multiprobe Solutions and Non-Convex Optimization.

Phase reconstruction is in general a non-trivial problem when it comes to devices where the reference is not accessible. A non-convex iterative optimization algorithm is proposed in this paper in order to reconstruct the phase in reference-less spherical multiprobe measurement systems based on a rotating arch of probes. The algorithm is based on the reconstruction of the phases of self-transmitting devices in multiprobe systems by taking advantage of the on-axis top probe of the arch. One of the limitations of the top probe solution is that when rotating the measurement system arch, the relative phase between probes is lost. This paper proposes a solution to this problem by developing an optimization iterative algorithm that uses partial knowledge of relative phase between probes. The iterative algorithm is based on linear combinations of signals when the relative phase is known. Phase substitution and modal filtering are implemented in order to avoid local minima and make the algorithm converge. Several noise-free examples are presented and the results of the iterative algorithm analyzed. The number of linear combinations used is far below the square of the degrees of freedom of the non-linear problem, which is compensated by a proper initial guess. With respect to noisy measurements, the top probe method will introduce uncertainties for different azimuth and elevation positions of the arch. This is modelled by considering the real noise model of a low-cost receiver and the results demonstrate the good accuracy of the method. Numerical results on antenna measurements are also presented. Due to the numerical complexity of the algorithm, it is limited to electrically small- or medium-size problems.

Testing the Performance of Multi-Frequency Low-Cost GNSS Receivers and Antennas.

Global Navigation Satellite System (GNSS) low-cost multi-frequency receivers are argued as an alternative to geodetic receivers for many applications. Calibrated low-cost antennas recently became available on the market making low-cost instruments more comparable with geodetic ones. The main goal of this research was to evaluate the noise of low-cost GNSS receivers, to compare the positioning quality from different types of low-cost antennas, and to analyze the positioning differences between low-cost and geodetic instruments. The results from a zero baseline test indicated that the u-blox multi-frequency receiver, namely, ZED-F9P, had low noise that was at the sub-millimeter level. To analyze the impact of the antennas in the obtained coordinates, a short baseline test was applied. Both tested uncalibrated antennas (Tallysman TW3882 and Survey) demonstrated satisfactory positioning performance. The Tallysman antenna was more accurate in the horizontal position determination, and the difference from the true value was only 0.1 mm; while, for the Survey antenna, the difference was 1.0 mm. For the ellipsoid height, the differences were 0.3 and 0.6 mm for the Survey and Tallysman antennas, respectively. The comparison of low-cost receivers with calibrated low-cost antennas (Survey Calibrated) and geodetic instruments proved better performance for the latter. The geodetic GNSS instruments were more accurate than the low-cost instruments, and the precision of the estimated coordinates from the geodetic network was also greater. Low-cost GNSS instruments were not at the same level as the geodetic ones; however, considering their cost, they demonstrated excellent performance that is sufficiently appropriate for various geodetic applications.

Feasibility of Using Low-Cost Dual-Frequency GNSS Receivers for Land Surveying.

Global Navigation Satellite Systems (GNSS) have revolutionized land surveying, by determining position coordinates with centimeter-level accuracy in real-time or up to sub-millimeter accuracy in post-processing solutions. Although low-cost single-frequency receivers do not meet the accuracy requirements of many surveying applications, multi-frequency hardware is expected to overcome the major issues. Therefore, this paper is aimed at investigating the performance of a u-blox ZED-F9P receiver, connected to a u-blox ANN-MB-00-00 antenna, during multiple field experiments. Satisfactory signal acquisition was noticed but it resulted as >7 dB Hz weaker than with a geodetic-grade receiver, especially for low-elevation mask signals. In the static mode, the ambiguity fixing rate reaches 80%, and a horizontal accuracy of few centimeters was achieved during an hour-long session. Similar accuracy was achieved with the Precise Point Positioning (PPP) if a session is extended to at least 2.5 h. Real-Time Kinematic (RTK) and Network RTK measurements achieved a horizontal accuracy better than 5 cm and a sub-decimeter vertical accuracy. If a base station constituted by a low-cost receiver is used, the horizontal accuracy degrades by a factor of two and such a setup may lead to an inaccurate height determination under dynamic surveying conditions, e.g., rotating antenna of the mobile receiver.